Nano-Machines Behave Like Human Muscle

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Introduction

Recently, a research team from the Centre National de la Recherche Scientifique (CNRS) in France, led by Nicolas Giuseppone and working at laboratories across the country, have come up with a breakthrough innovation in the field of nanoscience - assembly of nano-machines into structures that can produce coordinated contraction movement resembling the movement of muscular fibers in humans.

In another innovative breakthrough, scientists from UC Santa Barbara, Omar Saleh, and Deborah Fygenson worked together to create a dynamic gel that is made of DNA and can mechanically respond to stimuli just the way human cells would do. The gel has been aptly termed ‘smart material’.

The DNA gel contains stiff DNA nanotubes that are connected to each other via long, pliable DNA linkers. FtsK50C, a motor protein, helps to bind to special sites on the linkers. In order to draw the nanotubes together and stiffen the gel, ATP, a biochemical fuel, is introduced to the gel, which helps the motor molecules to reel in the linkers to which they are bound.

Both of these developments will have important consequences in various research fields, from robotics and medical prosthetics to in-depth research into the behaviour of complex nanostructured materials.

Development of Nano-Machines

Human muscles are controlled by the coordinated movement of thousands of protein fibres - natural nano-machines. Proteins in nature are capable of performing functions such transport of ions, synthesis of ATP and cell division, which are all essential parts of a living organism.

Nanotechnology research has begun to be able to mimic these functions with man-made nano- machines. However, there are limitations; these machines can only function individually over distances of the order of a nanometer.

This is where the work of Giuseppone’s team comes in. They were able to combine thousands nano-machines, each capable of telescopic motion of about 1nm, and amplify their movement in a well-coordinated manner. The team achieved this by first synthesizing long polymer chains via supramolecular bonds. The simultaneous movements of the nano-machines were influenced by pH so as to enable the polymer chains to contract or extend about 10 µm, thus magnifying the movement by a factor of 10,000.

The bacterial motor protein, FtsK50C, allowed the scientists to enable the gel to contract and stiffen in the same way cytoskeletons react to the motor protein myosin. To monitor the movement of the gel, they fixed a tiny bead to its surface and calculated its position before and after activation with the motor protein. The gel was found to have similar active variations and mechanics to that of cells. Just like a cell uses adenosine triphosphate (ATP) for energy, this smart DNA gel uses ATP for movement.

This gel’s innovation stands out as the use of ATP promotes faster and stronger mechanics than other smart gels based on synthetic polymers. It can now be used to study further about how cytoskeletons work.

A gel made up of stiff DNA nanotubes and flexible DNA linkers can be made stiff of flexible using ATP as a chemical trigger. Image credit: Peter Allen, UCSB.

What are Supramolecular Polymers?

Polymers are long molecular chains, consisting of many repeating units connected by covalent chemical bonds. Supramolecular polymers are slightly different in structure, however. They are still made up of arrays of monomer units, but they are bound together by relatively weak, reversible, non-covalent bonds, e.g. hydrogen bonds.

The directions and strengths of the bonds are finely tuned to ensure that the array of molecules act as a polymer. The reversibility of the non-covalent bonds means that the supramolecular polymers are only formed under certain conditions, and the lengths of the chains are directly linked to the temperature, the strength of the non-covalent bond, and the concentration of the monomer.

In the work done by the CNRS scientists, the tuneability of supramolecular polymers was used to create structures that would behave in exactly the required way - in this case, allowing the monomer units to physically interact, to combine their individual movements into a coherent action on a much larger scale.

Applications of Artificial Muscles

This innovative biomimetic discovery has the potential for use in scores of robotic applications, nanotechnology and medicine. It can also be used to further develop materials and technologies incorporating nano-machines.

The smart gel project by UC Santa Barbara scientists will also be a significant contribution to development of artificial muscles, as they can replicate the controlled contractions which are fundamental to how human muscle works. They can also be applied to wide range of fields such as smart materials, cytoskeletal mechanics and nonequilibrium physics research, and DNA nanotechnology.

The chief application of artificial muscles is in prosthetics and strength-assist devices.

However, the viscoelastic nature allows artificial muscles to act as suspension systems, thereby eliminating the need for external suspension. The soft nature allows it to be comfortably used in humans without causing injury. The miniaturisability of the artificial muscles makes them perfect for small, portable equipment, e.g. cameras.

Experts state that these discoveries will have significant wide-reaching and long-term implications in soft-materials science and engineering, and in our understanding of nanomaterials.